The program on analysis of gonadotropin receptors and actions of gonadotropic hormones is an important component of the Endocrinology and Reproduction Research Branch scientific research objectives. This program is supported by a Contract that provides large amounts of well characterized preparations including purified gonadal cells, various short term and established cell cultures, gonadal tissues and cell fractions, and receptor preparations. Gonadal cells are prepared acutely from a large number of control animals and under multiple protocols. The contract supports work in reproductive biology allowing investigators to perform studies on the binding characteristics of gonadotropin and prolactin receptors of testicular, ovarian, Nb2 lymphoma and several transfected cells, and cell membranes; and of the biological characterization of LH and related hormones, and studies on the mechanisms of hormone-receptor interaction, signal transduction, interaction between signalling pathways, and modulation of key metabolic steps of the androgen biosynthetic pathways.